linux-kernel - Re: [PATCH v3 18/77] ncr5380: Eliminate USLEEP

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Date:	Tue, 22 Dec 2015 08:05:02 +0100
From:	Hannes Reinecke <hare@...e.de>
To:	Finn Thain <fthain@...egraphics.com.au>,
	"James E.J. Bottomley" <JBottomley@...n.com>,
	Michael Schmitz <schmitzmic@...il.com>,
	linux-m68k@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: [PATCH v3 18/77] ncr5380: Eliminate USLEEP_WAITLONG delay

On 12/22/2015 02:17 AM, Finn Thain wrote:
> Linux 2.1.105 introduced the USLEEP_WAITLONG delay, apparently "needed for
> Mustek scanners". It is intended to stall the issue queue for 5 seconds.
> There are a number of problems with this.
>
> 1. Only g_NCR5380 enables the delay, which implies that the other five
>     drivers using the NCR5380.c core driver remain incompatible with
>     Mustek scanners.
>
> 2. The delay is not implemented by atari_NCR5380.c, which is problematic
>     for re-unifying the two core driver forks.
>
> 3. The delay is implemented using NCR5380_set_timer() which makes it
>     unreliable. A new command queued by the mid-layer cancels the delay.
>
> 4. The delay is applied indiscriminately in several situations in which
>     NCR5380_select() returns -1. These are-- reselection by the target,
>     failure of the target to assert BSY, and failure of the target to
>     assert REQ. It's clear from the comments that USLEEP_WAITLONG is not
>     relevant to the reselection case. And reportedly, these scanners do
>     not disconnect.
>
> 5. atari_NCR5380.c was forked before Linux 2.1.105, so it was spared some
>     of the damage done to NCR5380.c. In this case, the atari_NCR5380.c core
>     driver was more standard-compliant and may not have needed any
>     workaround like the USLEEP_WAITLONG kludge. The compliance issue was
>     addressed in the previous patch.
>
> If these scanners still don't work, we need a better solution. Retrying
> selection until EH aborts a command offers equivalent robustness. Bugs in
> the existing driver prevent EH working correctly but this is addressed in
> a subsequent patch. Remove USLEEP_WAITLONG.
>
> Signed-off-by: Finn Thain <fthain@...egraphics.com.au>
>
> ---
>   drivers/scsi/NCR5380.c   |   19 +++++--------------
>   drivers/scsi/g_NCR5380.c |    1 -
>   2 files changed, 5 insertions(+), 15 deletions(-)
>
> Index: linux/drivers/scsi/NCR5380.c
> ===================================================================
> --- linux.orig/drivers/scsi/NCR5380.c	2015-12-22 12:15:51.000000000 +1100
> +++ linux/drivers/scsi/NCR5380.c	2015-12-22 12:15:52.000000000 +1100
> @@ -468,10 +468,6 @@ static void NCR5380_print_phase(struct S
>   #ifndef USLEEP_POLL
>   #define USLEEP_POLL msecs_to_jiffies(200)
>   #endif
> -#ifndef USLEEP_WAITLONG
> -/* RvC: (reasonable time to wait on select error) */
> -#define USLEEP_WAITLONG USLEEP_SLEEP
> -#endif
>
>   /*
>    * Function : int should_disconnect (unsigned char cmd)
> @@ -619,8 +615,8 @@ static void prepare_info(struct Scsi_Hos
>   	         "can_queue %d, cmd_per_lun %d, "
>   	         "sg_tablesize %d, this_id %d, "
>   	         "flags { %s%s%s%s}, "
> -#if defined(USLEEP_POLL) && defined(USLEEP_WAITLONG)
> -		 "USLEEP_POLL %lu, USLEEP_WAITLONG %lu, "
> +#if defined(USLEEP_POLL) && defined(USLEEP_SLEEP)
> +		 "USLEEP_POLL %lu, USLEEP_SLEEP %lu, "
>   #endif
>   	         "options { %s} ",
>   	         instance->hostt->name, instance->io_port, instance->n_io_port,
> @@ -631,8 +627,8 @@ static void prepare_info(struct Scsi_Hos
>   	         hostdata->flags & FLAG_DTC3181E      ? "DTC3181E "      : "",
>   	         hostdata->flags & FLAG_NO_PSEUDO_DMA ? "NO_PSEUDO_DMA " : "",
>   	         hostdata->flags & FLAG_TOSHIBA_DELAY ? "TOSHIBA_DELAY "  : "",
> -#if defined(USLEEP_POLL) && defined(USLEEP_WAITLONG)
> -	         USLEEP_POLL, USLEEP_WAITLONG,
> +#if defined(USLEEP_POLL) && defined(USLEEP_SLEEP)
> +	         USLEEP_POLL, USLEEP_SLEEP,
>   #endif
>   #ifdef AUTOPROBE_IRQ
>   	         "AUTOPROBE_IRQ "
Wouldn't it make more sense to remove the USLEEP_WAITLONG completely?
 From what I can see it is meant to indicate that WAITLONG is enabled,
but we've just removed that functionality...

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@...e.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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